This application claims priority to DE 10 2007 039 926.1 filed on Aug. 23, 2007. The entire disclosure of the prior application/applications is considered to be part of the disclosure of the instant application and is hereby incorporated by reference.
The present invention concerns a method and a device for the cleaning of flue gases, in particular for the separation of sulphur dioxide (SO2) from flue gas and at the same time prevention of the releasing of ammonia (NH3) and the formation of aerosols at ammonium sulphate resulting therefrom.
From the prior art several methods for the cleaning of waste gases are known. For example a process for the removal of sulphur dioxide from flue gases is described in DE 37 33 319 C2. It concerns a three-stage counter current scrubber process for the separation of sulphur dioxide, in which after a dust-filter and a quench scrubber step for the separation of hydrochloric acid and hydrofluoric acid by means of washing with water the three-stage counter current device is set out. The first two steps of the sulphur dioxide scrubber process are operated by the addition of ammonia, in the third step sulphuric acid is added in order to separate released ammonia.
From DE 197 31 062 C2 a method for the separation of acidic gases from smoke gases is known, in particular from off-gases of power stations and off-gases of waste incinerators. A two-stage counter current scrubber process for the separation of sulphur dioxide is described. A dust filter and a quench/scrubber step are preset to the separation of sulphur dioxide for the removal of hydrochloric acid and hydrofluoric acid by washing with water. In the scrubber cycle of the first stage, ammonium sulfite/hydrogen sulfite is oxidised to ammonium sulphate with oxygen-containing gas.
EP 0 778 067 B1 discloses a device for the cleaning of smoke gases with different amounts of acidic components and methods for the operation of the device. After a dust filter and a quench/scrubber step for the separation of hydrochloric acid and hydrofluoric acid by washing with water a counter current scrubber process for the separation of sulphur dioxide is arranged.
EP 0 212 523 discloses a one-stage counter current scrubber process with the addition of ammonia and oxidation to sulphate by means of addition of air in the scrubber bottom.
The determination of SO2-concentration in off-gases by means of absorption in an aqueous solution of hydrogen peroxide (H2O2) is described in the VDI Rule 2462, journal 2.
DE 40 36 899 C2 and U.S. Pat. No. 3,760,061 disclose a cleaning process of flue gas for the separation of SO2 by means of hydrogen peroxide whereby sulphuric acid is formed.
With the previously known scrubber methods exclusively by means of ammonia, the separation of sulphur dioxide succeeds only incompletely because low pH-values have to be used in order to prevent the release of ammonia. By means of the addition of sulphuric acid in a third scrubber stage (DE 37 33 319 C2), the ammonia released from the two preset ammonia scrubber stages can be separated. However, in the case of such acid scrubber solutions, nearly no separation of SO2 takes place. In addition to the costs for the necessary sulphuric acid, in particular the additional costs for cleaning and for disposal of the ammonia charge generated by means of the feeding of sulphuric acid, are disadvantageous. These economical facts are important in particular when using this method in waste incinerators.